Applications of Light & Lenses
Cameras
What are the three basic components of a traditional analogue camera?
Leon just found his grandma’s photo album. There are photographs from a family picnic, of him and Lina when they were babies... Even photographs from his parents' wedding! Looking at these photographs is like looking into the past! Our eyes and brains process the light reflected from different objects.
In this way we experience the world around us as visual images. What you see can become a memory, but never a physical object, like a photograph. To capture moments and images as photographs, you need a camera. Cameras process images much like our eyes do, but they also record them as pictures. Let’s see how this happens!
Traditional analogue cameras consist of three basic elements. The first, at the very front, is the optical element – the lens. In its simplest form, a camera lens is just a single, curved piece of glass. But more advanced cameras often have several such lenses, enclosed in some kind of tube – the photographic lens or photographic objective. Just like your eyes, the lens collects light rays coming from different directions.
The curved shape of the lens causes light rays to bend and focus, so that they form a real image of what you see in front of the camera. But the image is flipped upside down! The lens is attached to the second basic element of the camera - the body. The body is a sealed box, with an opening on one side. The opening is needed to let light collected by the lens enter the camera.
Inside the body, there is an important mechanical element, which acts like shutters on a window. Its role is to block the light. This is the camera’s shutter. When you press the camera button, the shutter opens and exposes the third basic element of the analogue camera - the photographic film. The photographic film is a chemical component.
It is a strip of very thin plastic, coated with chemicals that are sensitive to light. When exposed to light, these chemicals on the photographic film undergo a chemical reaction, which records the image. For the final image to look good, you need to adjust the amount of light that falls onto the film. The amount of light can be adjusted in two ways. One is by deciding how long the shutter should be open — this is often referred to as shutter speed.
The other is by using a mechanism on the camera called a diaphragm. This mechanism regulates the size of the opening the light comes through. This opening is the aperture. Next, the image recorded on the photographic film needs to be developed onto paper, to create photographs. Just like those in Leon’s grandma’s photo album.
But Leon takes pictures with his mobile phone every day, and he doesn’t need to develop anything, ever! He just clicks and can watch the images on screen whenever he likes. This is because the camera in his mobile phone is a digital camera. In digital cameras, the chemical component of the camera is replaced by an electronic element. Instead of a photographic film, the light falls onto a light-sensitive digital sensor.
The sensor measures and records the pattern of light falling onto it, and saves this information on a memory card. You can see the picture on the digital screen instantly. And you can still print out your digital photos if you want to make your own album, Leon!